I use a lot of Lee Collets and this is the way I adjust them
Adjust the lock nut all the way to the top of the threads
this will put the lever in the most horizontal position
which makes it easier to gauge the pounds of weight you are putting on the lever.
The Lee instructions say to not cam the press over or hit the bottom of the stroke. On most presses it says to thread the die in 2 full turns after it hits the shell holder. That accomplishes the same thing but the lever is angled downward more.
Lee used to ship undersize mandrels for $5.00 each
They are much better IMO because it is hard to get 100% consistant diameter if you reduce the mandrel yourself. If you get the part of the mandrel exactly where you want it where the neck is compressed against it, when withdrawn a slight oversize or lopsided mandrel closer to the decapper will expand the neck when it passes over it.